A passenger ferry operated by Shosen Yaeyama — the Yaeyamamaru (八重山丸) — completed its inaugural voyage last week, connecting Ishigaki Island in Okinawa Prefecture, Japan, to Keelung Port in northern Taiwan. The service restores a maritime passenger route suspended for 18 years since the Japanese operator Arimura Sangyo discontinued the Okinawa-to-Taiwan line — which ran via Miyako Island and Ishigaki — in 2008.
Beyond its role as a new gateway for tourism between Japan and Taiwan, Ishigaki Island has over the past decade been transformed into a key node in Japan's southwestern defense perimeter, driven by growing concerns over Chinese military activity in the region.
The Japan Coast Guard — the functional equivalent of Taiwan's Coast Guard Administration (海巡署) — has deployed 14 medium-to-large patrol vessels at Ishigaki, more than at any other base nationwide. The island's strategic importance stems in part from geography: it lies approximately 270 kilometers from Keelung, but roughly 400 kilometers from Okinawa's main island.
Senkaku Patrol Unit and the Coast Guard Build-Up
Japan established a dedicated Senkaku patrol unit at Ishigaki in 2016 in response to China's intensifying coast guard presence and non-military harassment in the East China Sea. Incidents in recent years had sharpened Tokyo's concern — Japanese fishing vessels operating near the Senkakus had been shadowed by Chinese coast guard ships, and collisions with Japan Coast Guard patrol vessels had been reported. The Senkaku Islands lie approximately 170 kilometers from Ishigaki, compared to more than 400 kilometers from Okinawa's main island, making Ishigaki the natural base for this mission.
The largest vessel stationed at Ishigaki is the 6,500-ton helicopter patrol ship Asazuki (あさづき, PLH-35). The remaining 13 vessels range from 1,000 to 5,500 tons. Japan Coast Guard's 2025 annual report confirms that only Kagoshima and Ishigaki have ten or more large patrol vessels deployed — underscoring the southwestern maritime corridor's elevated security status.
Japan Steadily Strengthens Military Build-Up Across the Southwest Islands
Japan's 2024 Defense White Paper documents a sustained military build-up across the Southwestern Islands since 2016. In 2023, the Japan Ground Self-Defense Force (JGSDF) established the Yaeyama garrison on Ishigaki, deploying both anti-ship and surface-to-air missile systems.
Yonaguni Island — Japan's westernmost territory, located approximately 110 kilometers from Taiwan's Yilan County — has undergone a parallel expansion. The JGSDF established a coastal surveillance unit there in 2016. The Japan Air Self-Defense Force deployed a mobile air defense radar in 2022, and an electronic warfare unit was added in 2024.
The strategic logic behind Japan's build-up is reinforced by a pattern of Chinese and Russian naval activity in the region. According to research by Wang Tsun-yen (王尊彥), assistant research fellow at the Institute for National Defense and Security Research's Division of National Security Studies, People's Liberation Army Navy vessels have transited the Miyako Strait — between Miyako Island and Okinawa's main island — on multiple occasions in recent years. In April and May 2021, Chinese naval forces conducted what Wang described as a "quasi-circumnavigation" exercise around Miyako and Yonaguni Islands.
The activity has continued. In April of this year, two PLA Navy vessels transited the channel between Iriomote Island and Yonaguni Island, according to Japan's Ministry of Defense. In mid-May, multiple Russian naval vessels and cargo ships passed through the same waterway.
The Yaeyama Islands lie just over 100 kilometers from Taiwan's northeastern coastline.
U.S.-Japan Joint Exercises Now Encompass the Yaeyama Islands
Military exercises between the JGSDF and U.S. forces in Japan have progressively expanded into the Yaeyama archipelago. In mid-May, the JGSDF conducted its "Ground Component Command Exercise," designed to strengthen command-and-control and logistics capabilities across Miyako, Ishigaki, and Yonaguni Islands. A U.S. Marine Corps Littoral Regiment based in Okinawa participated.
A further exercise — Resolute Dragon 26 — is scheduled from June 20 to 30, with an operational area spanning Kyushu through the Southwestern Islands, including Ishigaki and Yonaguni. Both the JGSDF and Japan Air Self-Defense Force are slated to participate alongside U.S. Marines.
Senior U.S. and Japanese Officials Have Visited the Forward Positions
The islands' strategic profile has attracted senior-level attention from both Tokyo and Washington. In November 2021, then-Commander of U.S. Indo-Pacific Command Admiral John Aquilino visited Yonaguni Island to observe Japan's defense installations firsthand.
Japan's current Defense Minister Koizumi Shinjiro (小泉進次郎) conducted his own inspection tour of Ishigaki, Miyako, and Yonaguni in November of last year. According to the Ministry of Defense's official social media account, Koizumi received operational briefings, inspected facilities and equipment, met with Self-Defense Force personnel, and observed a live scramble exercise involving fighter jets responding to an unidentified airspace incursion — viewed from his aircraft.
"Through this inspection, I gained a clear understanding of the actual conditions faced by the personnel stationed in the southwestern region, and reaffirmed the importance of the mission they carry out here," Koizumi said.
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